Mitt Romney is to make a semi-official declaration of victory in the Republican presidential nomination race, accelerating the preparations for his battle against Barack Obama for the White House.

Romney is expected to pick up the bulk of the 200-plus delegates at stake in Tuesday's primaries in Pennsylvania, Delaware, New York, Connecticut and Rhode Island.

The contests are largely irrelevant after the departure of Romney's last serious challenger, Rick Santorum. But they provide him with a platform to make a nationally-televised speech, which will have the title: A Better America Begins Tonight.

His campaign team is billing it as a major speech that begins the process of drawing distinctions between him and Obama. Ryan Williams, a spokesman for the Romney campaign, said: "We're bringing the nomination process to a close and will kick off the general election."

Over the last year, Romney's message has been heavily tilted rightwards to appeal to the Republican base, and now he has to shift his appeal to the centre to attract the swing voters who will decide the general election.

In a sign that Romney regards the Republican race as over, he is not making his speech in any of the five states where the primaries are being held or in one of the upcoming races. Instead, he is holding it in New Hampshire, which voted in January and whose significance is purely symbolic, as the state where he launched his presidential bid in June last year.

Romney cannot formally declare victory in the Republican race, given that former House speaker Newt Gingrich and Texas congressman Ron Paul are still candidates, even though neither has any chance of catching him.

The results will move Romney closer to the 1,114 delegates he needs for a majority at the party conference in Tampa, Florida, in August, where he will be formally declared the Republican challenger for the presidency.

But with Gingrich and Paul still in the race, it could be weeks yet before he reaches the winning post.

Romney would receive a significant boost if Gingrich were to quit the race on Tuesday night, after the primary results. Although there have been confused messages in the last week about his intentions, Gingrich says he will remain in the race until Romney reaches the 1,114 mark.

He is to make his post-election speech in Charlotte, North Carolina, which holds its primary on 8 May.

As part of the shift from primary to general election mode, Romney is planning to merge his campaign team shortly with the Republican party national committee to prepare for the general election.

The Republican party hierarchy is keen to get on with general election planning and is reluctant to cede any more time or fundraising to the Obama re-election team. Romney discussed details of the merger with the Republican chairman, Reince Priebus, in Scottsdale, Arizona, last weekend.

In 2008, John McCain's campaign team and the Republican national committee failed to mesh, but Romney already has senior members of this campaign team on the national committee.

Romney's campaign team is not bothered about the niceties of Gingrich and Paul still being in the race and intends to appoint more senior members of his campaign staff to the national committee to ensure the smooth co-ordination of efforts.

The national committee, as well as supporting Romney's White House bid, is also responsible for helping with congressional races being held in November.Romney's campaign team will be the dominant part of the operation but the Republican national committee will have a substantial fundraising effort of its own and will channel some of those funds to Romney. It also has a network of volunteers who will help get the vote out in November.